Welcome to the community.
This only works for Apps that directly support split screen working. To open a second instance of the same App:
- With the App running in the foreground, swipe-up from the bottom edge of the screen - just enough to make the dock visible (don’t flick as this will return you to the last used home screen; similarly, don’t swipe up and pause before lifting your finger - as this will invoke the task switcher).
- Drag the App that you wish to run in split screen, from the dock, to either side of the screen - then release; the second App (or second instance of the same App) will open in split screen. Dragging to the extreme edge will open the second App/instance in slide-over mode.
I recommend downloading the iPad User Guide for iPadOS within the Apple Books App. It’s free - and will teach you everything you need to know about the new gestures, multi-tasking - and all the cool new features of iPadOS.
I hope this helps - and resolves your questions.